Build predicate for EfCore IQueryable.Where<T>

Question

I'd like to make a Search<T> extension method for IQueryable, but getting a LINQ expression runtime error, which cannot be translated.

public static IQueryable<T> Search<T>(this IQueryable<T> source, Func<T, string> expression, string search)
{
    if (source == null)
        throw new ArgumentNullException(nameof(source));

    if (string.IsNullOrWhiteSpace(search))
        return source;

    return source.Where(x => EF.Functions.Like(expression(x), $"%{search}%"));
}

Usage:

dbContext.People.Search(x => x.Name, "Joe").ToList();

I guess the wrong line is the expression(x), but what is the correct way?

Answer 1

It doesn't use the Like function, but works fine as an extension.

var result = dbContex.Currencies.Search(x=>x.Symbol, "EUR").ToList();


public static IQueryable<T> Search<T>(this IQueryable<T> source,  Expression<Func<T,string>> expression, string search)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));

            if (string.IsNullOrWhiteSpace(search))
                return source;
            var method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
            var value = Expression.Constant(search, typeof(string));
            var exp1 = Expression.Call(expression.Body, method, value);
            var ex2 = Expression.Lambda<Func<T, bool>>(exp1, expression.Parameters[0]);
            

            return source.Where(ex2);
        }